It has become increasingly important to manage power consumption in many common consumer products. Reducing power consumption is important for several reasons. For one thing, generating the power needed to operate the multitude of consumer products creates a strain on the environment. For example, the power generation plants currently used to generate electrical power needed by consumers create greenhouse gases that may be contributing to global warming.
In order to control the amount of power consumed, the governments of many countries around the world are creating programs designed to reduce the amount of energy consumed by their populations. One such program is ENERGY STAR in the US. Another is Code of Conduct in the European Union. ENERGY STAR is a U.S. Environmental Protection Agency voluntary program that helps businesses and individuals save money and protect the environment through superior energy efficiency. ENERGY STAR provides guidelines for maximum power consumption and rates products based on their ability to meet these guidelines. It is very desirable for all types of products to achieve high ratings from ENERGY STAR and the other programs around the world. Therefore, reducing power consumption is an important goal for all manufacturers of consumer electronics.
Set top boxes (STBs) are one type of consumer electronic device. STBs are devices that receive, decode, process and provide video for display on a television or other display device. Typically, a cable television service provider gives one or more set top boxes to a cable service subscriber to allow the subscriber to receive and display the content transmitted to the subscriber by the service provider. When a subscriber choices to watch content provided by the service provider (i.e., when the subscriber wants to watch television), the subscriber will tune the STB to the channel that has the desired content or search through a memory of stored content and select the desired content for viewing. Several processes are implemented in the course of receiving, decoding, processing and displaying the content. Therefore, a relatively sophisticated processor is used within the STB to perform these functions. The sophistication of the processor results in a relatively long initial “boot-up” time when the STB is first turned on. Therefore, it is desirable to keep the STB powered up at all times. However, the amount of power consumed by a STB is relatively high. Clearly, this runs counter to the goal of reducing power consumption.
In many consumer electronic products, methods for reducing the power consumption have been derived. Some of those methods include turning off particular functions when they have not been used for a prolonged amount of time. For example, many personal computers today allow a user to select power saving modes that can cause a video card or hard disk drive within the computer to enter into a reduced power consumption state. Once activity is detected, the computer will return the video card or hard disk drive back to a fully active state.
In some instances, consumer products include integrated circuit (IC) chips that perform several functions. When these functions are performed by different physical portions of the IC chip, a power saving mode can be implemented whereby particular functions within the IC chip are turned off, thus reducing the overall power consumption of the IC chip. These functions can either be turned off directly by the user placing the device in standby mode or by a timer that determines that the function has not been used for some predetermined amount of time. These functions can then be turned back on when the user makes a request for one of the functions that was turned off.
In some cases, power is not removed from the sections of the IC, but rather the function is simply inactive. Simply deactivating a function typically will reduce the amount of power consumed by the IC. However, when power is applied to the circuits of the IC, even if a particular circuit is inactive, some power will typically still be consumed. Therefore, some ICs are designed with an “always-on power island” that isolates those circuits that need to remain on from those circuits that can be turned off during periods of inactivity. Such always-on power islands allow the power to continue to be applied to those circuits responsible for the functions that need to remain on, even during inactive periods. However, the use of such an always-on power island allows power to be completely removed from those circuits that are not on the always-on island (i.e., those circuits for which power can be removed in order to conserve power and reduce power consumption during inactive periods).
A switch is used to shut off power to the non-essential circuits that do not reside within the always-on power island. The switch lies between the power structures that provide power to circuits within the always-on power island and the power structures that provide power to the circuits that are not within the always-on power island, thereby isolating the power within the always-on power island. The use of an always-on power islands provides an effective means for removing power from non-essential circuits while allowing essential circuits to remain fully powered.
Typically, when power is removed from a processor or the processor is placed in an inactive state, there is a need to save information to allow the processor to return to an active state. In some cases, it is desirable for the processor to continue operation from the state that existed within the processor when the processor was interrupted. There are several types of memory devices, each of which have certain characteristics that make them more or less desirable in different instances. Typical solid state Random Access Memory (RAM) is very fast. RAM makes information readily available to a processor. Alternatively, Flash memory provides a means for storing larger amounts of information inexpensively, but at slightly slower speeds than can typically be accomplished with RAM. Magnetic disk drives are used to store large amounts of information and have relatively slow read times.
While the use of standby modes and other techniques for deactivating non-essential circuits have reduced power consumption significantly, the desire to further reduce power consumption requires more and more efficient use of power. Therefore, even these techniques are insufficient to provide the desired reduction in power consumption. With smaller integrated circuit geometries it becomes even harder to meet low power consumption goals. This is particularly true when the geometries are below 40 nm, where the static leakage currents are high. High leakage currents increase the power consumption, even in inactive/standby modes. Accordingly, there is presently a need for methods and apparatuses that can further reduce power consumption.